The electrophilic substitution activity of aromatic compounds depends on substituents. The stronger the electron donating ability of substituents, the higher the activity, and the nitro group is a strong electron withdrawing group, so the reaction activity is the weakest. Alkyl and amino groups are electron-donating groups, but the nitrogen on the amino group has a lone electron pair, which has strong electron-donating ability. Answer c, there is an electron-donating group and an electron-withdrawing group, so the reaction activity is in the middle, and the order should be d > a > c > b.

The third problem: the stability of cyclohexane mainly depends on the number of substituted horizontal bonds and vertical bonds. The more horizontal keys, the more stable they are. A is the most unstable with all vertical bonds, D is the most stable with all horizontal bonds, BC is a vertical bond and a horizontal bond, but the steric hindrance of B is large, so the order of stability is D > C > B > A.